Reference for Pesachim 124:3
ואיבעית אימא כולה בטומאת בשר והיכא הותרה בטומאת פסח דתנן פסח הבא בטומאה נאכל בטומאה שלא בא מתחילתו אלא לאכילה
For we learned: The Paschal lamb which comes [if offered] in uncleanness is eaten in uncleanness, for at the very outset it did not come for [aught] except to be eaten.<span class="x" onmousemove="('comment',' V. infra 76a.');"><sup>2</sup></span> R'Huna son of R'Joshua raised an objection: If a Paschal lamb has passed its year<span class="x" onmousemove="('comment',' It became a year old on the first of Nisan, and was then set aside for the Passover sacrifice. Since a year is the extreme limit for such (v. Ex. XII, 5: a male of the first year) , it automatically stands to be a peace-offering, being unfit for its original purpose.');"><sup>3</sup></span> and he [its owner] slaughtered it at its own time<span class="x" onmousemove="('comment',' I.e., on the eve of Passover.');"><sup>4</sup></span>